Peritoneal dialysis (PD) is an effective home-based dialysis treatment modality for patients with severe renal disease, and it has been used in many countries as a significantly lower cost alternative to hemodialysis. However, the success of PD may be compromised by complications related to the catheter, which is usually made of silicone. Biofouling (in the form of protein adsorption and cell adhesion) and microbial (bacterial and fungal) attachment on the highly hydrophobic silicone surface may result in omental wrapping and infection, which is the leading cause of PD outflow failure and the second most common cause of death for PD patients, respectively. In addition, when in contact with blood, platelet adhesion and activation-induced thrombosis may lead to intraluminal obstruction of PD catheters. The PD catheter can be considered the “lifeline” of the PD patient, and catheter-related complications are the primary obstacle to the widespread use of PD. Since the introduction of a Tenckhoff catheter in mid-1960s, the development of new PD catheter designs has not shown convincing improvement in reducing infection and increasing the survival rates of PD patients.1 Thus, in recent years, modification of the catheter surface to improve its antifouling, antibacterial and hemocompatible properties has attracted increasing interest.2 
Another type of catheter, the central venous catheter (commonly made of polyurethane or silicone), is widely used clinically for administering medication, withdrawal of blood samples and hemodialysis treatment. Microbial colonization can occur readily either on the inside or outside of these indwelling catheters, and catheter-associated bloodstream infections (CABSIs) resulting from use of such vascular access devices remain a major clinical problem with adverse effects on patient morbidity, mortality, and healthcare cost. A similar situation arises from the use of indwelling urinary catheters (usually made of silicone), which are standard medical devices in hospital and nursing home settings. Catheter-associated urinary tract infections (CAUTIs) are the commonest hospital-acquired infection worldwide. Thus, surface modification of catheters to inhibit microbial colonization would be highly beneficial in combating CABSIs and CAUTIs.
Tethering of functional polymer coatings via covalent bonding provides an effective way to modify catheter surface properties. The synthetic hydrophilic polymer, poly(ethylene glycol) (PEG), and its derivatives are the most widely used antifouling and antibacterial materials. However, PEG suffers from some limitations: PEG-coated surfaces are unable to reduce protein adsorption to very low levels due to their interactions with proteins, and they are also susceptible to oxidative degradation in the presence of oxygen and transitional metal ions which limits their long-term antifouling and antibacterial performance in vivo. Other synthetic polymers such as poly(acrylamide)s, poly(sulfobetaine methacrylate),3,4 poly(carboxybetaine methacrylate) and poly(peptoid)s have been extensively investigated for use as antifouling coatings. Natural polymers, as compared with their synthetic counterparts derived from petrochemicals, provide an attractive alternative. Chitosan and its derivatives are the most widely used natural polymers for antibacterial coatings, but their antifouling properties are limited because of their strong interactions with proteins.5 Heparin (HEP), a commonly-used anticoagulant agent, has been reported to provide an antibacterial coating which can reduce infection both in vitro and in vivo.6 However, the antibacterial effect of HEP is still debatable. Some studies report that HEP does not significantly reduce biofilm formation by S. aureus and may even stimulate the process.7,8 Further, immobilization of protein-degrading enzymes, such as pronase and α-chymotrypsin, has been found to reduce protein adsorption on surfaces.9,10 
Agarose (AG) is a neutral polysaccharide, which is derived from agar. As a U. S. Food and Drug Administration (FDA) approved ingredient, AG is widely used in many fields of biomedical applications, such as nerve regeneration, drug and gene delivery, and dental impression due to its biocompatibility, stability and inertness. In earlier reports, AG, in the form of a film and hydrogel, was shown to resist Proteus mirabilis bacterial adhesion11 and marine fouling.12 
At present, surface modification of biomaterials such as silicone, polyurethane and titanium with covalently immobilized natural polymer coatings for the long-term improvement of its antifouling, antibacterial/antifungal and hemocompatible properties is lacking.